Heavy crude oil presents problems in oil recovery and production. Crude oils of low API gravity and crude oils having a high pour point present production problems both in and out of the reservoir. Extracting and refining such oils is difficult and expensive. In particular, it is difficult to pump heavy crude oil or move it via pipelines.
Recovery of heavy crude oils may be enhanced by heating the oil in situ to reduce its viscosity and assist in its movement. The most commonly used process today for enhanced oil recovery is steam injection, where the steam condensation increases the oil temperature and reduces its viscosity. Steam in the temperature range of 150 to 300 degrees Fahrenheit may decrease the heavy oil viscosity by several orders of magnitude. Cyclic steam simulation (CCS) is a method that consists of injecting steam into a well for a period of time and then returning the well to production. A recently developed commercial process for heavy oil recovery is steam assisted gravity drainage (SAGD), which finds its use in high permeability reservoirs such as those encountered in the oil sands of Western Canada. SAGD has resulted recovery of up to 65% of the original oil in places, but requires water processing. All such methods tend to be expensive and require the use of external water sources.
Other methods in current use do not require the use of water or steam. For example, processes such as the Vapex process, which uses propane gas, and naphtha assisted gravity drainage (NAGD) use solvents to assist in the recovery of heavy crude oils. The drawback to these processes is that the solvents—propane or naphtha—are high value products and must be fully recovered at the end of the process for it to be economical.
Yet another potential method to enhance the recovery of heavy crude oils is the Toe-To-Heel Injection (THAI) process proposed by the University of Bath. THAI involves both vertical wells and a pair of horizontal wells similar to that used in the SAGD configuration, and uses combustion as the thermal source. Thermal cracking of heavy oil in the porous media is realized, and the high temperature in the mobile oil zone provides efficient thermal sweeping of the lighter oil to the production well.
Even when they are recovered, heavy crude oils present problems in refinement. Heavy and light crude oil processing will give the same range of refined products but in very different proportions and quantities. Heavy oils give much more vacuum residues than lighter oils. These residues have an API between one and five and very high sulfur and metals content, which makes treatment difficult. Several processes exist to convert vacuum residues. They are thermal, catalytic, chemical, or combinations of these methods. Thermal processes include visbreaking, aquathermolysis and coking.
Solvent deasphalting (SDA) is a proven process which separates vacuum residues into low metal/carbon deasphalted oil and a heavy pitch containing most of the contaminants, especially metals. Various types of hydrotreating processes have been developed as well. The principle is to lower the carbon to hydrogen ratio by adding hydrogen, catalysis such as tetralin. The goal is to desulfurize and remove nitrogen and heavy metals. These processes may require temperature control, pressure control, and some form of reactor technology such as fixed bed, ebullated bed, or slurry reactor.
Recent concepts associate different processes to optimize the heavy crude conversion. For example, the combination of hydrotreating and solvent deasphalting in refineries or on site for partial upgrading of heavy crude may be used.
Finally, the process of gasification for upgrading heavy oil is used. It consists of conversion by partial oxidation of feed, liquid, or solid into synthesis gas in which the major components are hydrogen and carbon monoxide.
There is a need for an apparatus and method to enhance the recovery of heavy crude oils that does not suffer from the drawbacks associated with current methods. In particular, there is a need for a method that does not use steam or water from external sources, solvents that must be recovered, or combustion. Ideally, such an apparatus and method would at the same time assist in the in situ refinement of the heavy oil.
The present invention provides just such a method and apparatus. It utilizes radiofrequency energy to combine enhanced oil recovery with physical upgrading of the heavy oil.